min-storage advanced option does not compile with MPI

[jkwashbourne]

the operator in the MFE below does not compile when run with DEVITO_MPI=1

from devito import Grid, TimeFunction, Eq, Operator
grid = Grid(shape=(41,41,11))
p0 = TimeFunction(name='p0', grid=grid, time_order=2, space_order=8)
update_p = (p0.dx).dx + (p0.dy).dy + (p0.dz).dz 
op = Operator(Eq(p0.forward, update_p), name='MFE', opt=('advanced', {'min-storage': True}))
op.apply(time_M=10)

[mloubout]

Leads to gcc-related loop definition errors

fore 'x'
  191 |         for (int x = x0_blk0 - 4, xs = 0; x <= x0_blk0 + x0_blk0_size + 3; x += 1, xs += 1)
      |                                           ^
/var/folders/mx/qs0dn9rx7zn6dz2zvwv7tkk00000gn/T/devito-jitcache-uid501/229a49fd56fb5533d63a353d9945a04b9700d2be.c:211:45: error: expected iteration declaration or initialization before 'y'
  211 |           for (int y = y0_blk0 - 4, ys = 0; y <= y0_blk0 + y0_blk0_size + 3; y += 1, ys += 1)

Need to double check than icc still fine with this one